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|
package brotli
import (
"errors"
"io"
"github.com/andybalholm/brotli/matchfinder"
)
const (
BestSpeed = 0
BestCompression = 11
DefaultCompression = 6
)
// WriterOptions configures Writer.
type WriterOptions struct {
// Quality controls the compression-speed vs compression-density trade-offs.
// The higher the quality, the slower the compression. Range is 0 to 11.
Quality int
// LGWin is the base 2 logarithm of the sliding window size.
// Range is 10 to 24. 0 indicates automatic configuration based on Quality.
LGWin int
}
var (
errEncode = errors.New("brotli: encode error")
errWriterClosed = errors.New("brotli: Writer is closed")
)
// Writes to the returned writer are compressed and written to dst.
// It is the caller's responsibility to call Close on the Writer when done.
// Writes may be buffered and not flushed until Close.
func NewWriter(dst io.Writer) *Writer {
return NewWriterLevel(dst, DefaultCompression)
}
// NewWriterLevel is like NewWriter but specifies the compression level instead
// of assuming DefaultCompression.
// The compression level can be DefaultCompression or any integer value between
// BestSpeed and BestCompression inclusive.
func NewWriterLevel(dst io.Writer, level int) *Writer {
return NewWriterOptions(dst, WriterOptions{
Quality: level,
})
}
// NewWriterOptions is like NewWriter but specifies WriterOptions
func NewWriterOptions(dst io.Writer, options WriterOptions) *Writer {
w := new(Writer)
w.options = options
w.Reset(dst)
return w
}
// Reset discards the Writer's state and makes it equivalent to the result of
// its original state from NewWriter or NewWriterLevel, but writing to dst
// instead. This permits reusing a Writer rather than allocating a new one.
func (w *Writer) Reset(dst io.Writer) {
encoderInitState(w)
w.params.quality = w.options.Quality
if w.options.LGWin > 0 {
w.params.lgwin = uint(w.options.LGWin)
}
w.dst = dst
w.err = nil
}
func (w *Writer) writeChunk(p []byte, op int) (n int, err error) {
if w.dst == nil {
return 0, errWriterClosed
}
if w.err != nil {
return 0, w.err
}
for {
availableIn := uint(len(p))
nextIn := p
success := encoderCompressStream(w, op, &availableIn, &nextIn)
bytesConsumed := len(p) - int(availableIn)
p = p[bytesConsumed:]
n += bytesConsumed
if !success {
return n, errEncode
}
if len(p) == 0 || w.err != nil {
return n, w.err
}
}
}
// Flush outputs encoded data for all input provided to Write. The resulting
// output can be decoded to match all input before Flush, but the stream is
// not yet complete until after Close.
// Flush has a negative impact on compression.
func (w *Writer) Flush() error {
_, err := w.writeChunk(nil, operationFlush)
return err
}
// Close flushes remaining data to the decorated writer.
func (w *Writer) Close() error {
// If stream is already closed, it is reported by `writeChunk`.
_, err := w.writeChunk(nil, operationFinish)
w.dst = nil
return err
}
// Write implements io.Writer. Flush or Close must be called to ensure that the
// encoded bytes are actually flushed to the underlying Writer.
func (w *Writer) Write(p []byte) (n int, err error) {
return w.writeChunk(p, operationProcess)
}
type nopCloser struct {
io.Writer
}
func (nopCloser) Close() error { return nil }
// NewWriterV2 is like NewWriterLevel, but it uses the new implementation
// based on the matchfinder package. It currently supports up to level 7;
// if a higher level is specified, level 7 will be used.
func NewWriterV2(dst io.Writer, level int) *matchfinder.Writer {
var mf matchfinder.MatchFinder
if level < 2 {
mf = matchfinder.M0{Lazy: level == 1}
} else {
hashLen := 6
if level >= 6 {
hashLen = 5
}
chainLen := 64
switch level {
case 2:
chainLen = 0
case 3:
chainLen = 1
case 4:
chainLen = 2
case 5:
chainLen = 4
case 6:
chainLen = 8
}
mf = &matchfinder.M4{
MaxDistance: 1 << 20,
ChainLength: chainLen,
HashLen: hashLen,
DistanceBitCost: 57,
}
}
return &matchfinder.Writer{
Dest: dst,
MatchFinder: mf,
Encoder: &Encoder{},
BlockSize: 1 << 16,
}
}
|
